1. Field of the Invention
The present invention relates to a method of modifying a chemically amplified resist pattern for enhancing solvent resistance, resistance to exposure and development, or the like of a positive-type chemically amplified resist pattern, a modifier for a chemically amplified resist pattern to be used in the modifying method, and a resist pattern structure modified by the modifying method.
2. Description of the Related Art
The technologies central to fine processing process in manufacture of semiconductor integrated circuits and the like include photolithography and etching. In these technologies, first, a mask is produced which has a light blocking pattern corresponding to a pattern to be formed on a substrate, such as a circuit pattern. Then, by utilizing a precise photographic technology, the pattern drawn in the mask is transferred onto the substrate, whereby fine semiconductor devices, electrodes, wiring, etc. are fabricated with high productivity.
In practicing the photolithography, a functional material layer to be processed based on the pattern drawn in the mask is preliminarily formed in a film forming process precedent to the photolithography. The functional material layer is a layer of a material which, when processed, becomes a functional layer constituting the semiconductor devices, electrodes, wiring or the like. The functional material layer may be a semiconductor layer or insulator layer which is formed in a surface layer part of the substrate, or may be a conductive layer or semiconductor layer or insulator layer formed on the substrate in a laminated or stacked manner. Then, first, a photoresist layer (photosensitive material layer) is formed on the functional material layer. The photoresist, which commonly is composed of a photosensitive agent and a resin component or the like, is used in the form of a coating liquid prepared by dissolving or dispersing the ingredients thereof in an organic solvent. After the coating liquid is applied to the substrate by a coating method or the like, the solvent is evaporated off, to form the photoresist layer.
Next, using an exposure apparatus, the photoresist layer is selectively exposed to light through the mask, to form a latent image in the photoresist layer. Thereafter, unrequired portions of the photoresist layer are removed by development to make the latent image visible, whereby a photoresist layer patterned into a shape corresponding to the aperture pattern of the mask, that is, a resist pattern is obtained.
Subsequently, the functional material layer is etched using the resist pattern as a mask, whereby the functional material layer is patterned into the shape of the circuit pattern or the like, for forming the semiconductor devices, electrodes, wiring or the like.
Photoresists (photosensitive materials) are classified into two types, namely, the negative type and the positive type. In the negative type, the portions of the photoresist exposed to light are hardened through polymerization, so that by development the unexposed portions of the photoresist are dissolved away, leaving the exposed portions as a resist pattern. In the negative type, the resist pattern to be left may be swelled with the developing solution, leading to a lowering in resolution. In the positive type, on the other hand, portions of the photoresist exposed to light are depolymerized or changed into a structure soluble in the developing solution, so that by development the exposed portions of the photoresist are dissolved away, leaving the unexposed portions as a resist pattern. The positive type promises a high resolution. Therefore, for applications where high resolution is demanded, positive-type photoresists are used.
Meanwhile, the performances required of semiconductor apparatuses are being enhanced year by year, in terms of operating speed, the number of functions and the lowness of power consumption. To meet these requirements, the circuit patterns of semiconductor integrated circuits are continuously becoming finer. A stepper is used as an exposure apparatus at present. In addition, since the resolution of patterns which can be formed by exposure to light is restricted by the wavelength of the light used, the wavelength of the exposure light is becoming shorter and shorter.
Correspondingly to this trend, photoresists are required to have a sufficient sensitivity for exposure light of which the wavelength is becoming shorter, and to have a high resolution promising reproduction of fine patterns. In recent years, as photoresists having a sufficient sensitivity to short-wavelength light and capable of achieving a high resolution, chemically amplified resists have been used. A chemically amplified resist contains a photo acid generator (PAG) which generates an acid (hydrogen ion H+) when exposed to light, and a resin component the solubility of which is changed by the action of the acid.
FIGS. 14A to 14D illustrate examples of a component of a positive-type chemically amplified resist and a reaction thereof. Triphenylsulfonium trifluoromethanesulfonate shown in FIG. 14A is a photo acid generator which generates an acid (hydrogen ion H+) when exposed to light. On the other hand, polyhydroxystyrene derivative shown in FIG. 14B, hydroxystyrene-acrlyic acid copolymer derivative shown in FIG. 14C, hydroxystyrene-methacrylic acid copolymer derivative (not shown) [hereafter, acrylic acid and methacrylic acid together are abridged to (meth)acrylic acid], poly(meth)acrylic acid derivative (not shown) and the like are resin components each having a solubility which is changed by the action of an acid. Each of these resin components, in the state shown in the figure, has protecting groups bonded to part of acidic groups thereof and, therefore, is insoluble in alkaline developing solutions. However, the protecting groups are acid-detachable. Therefore, when hydrogen ions H+ are supplied from the photo acid generator, the linkage between the acidic group and the protecting group is hydrolyzed as shown in FIG. 14D. As a result, the acidic groups are regenerated. Accordingly, the above-mentioned resin components become soluble in alkaline developing solutions such as an aqueous solution of tetramethylammonium hydroxide (TMAH).
In the hydrolytic reaction shown in FIG. 14D, the hydrogen ion H+ functions as a catalyst and, therefore, the hydrogen ion is not lost in this reaction. Accordingly, one hydrogen ion generated from the photo acid generator exposed to light acts on the resin component repeatedly while diffusing, whereby the hydrolytic reaction is inducted many times. Thus, the chemically amplified resist is a resist having a mechanism in which one-time photoreaction is amplified by a multiplicity of runs of the acid-catalyzed reaction, which promises a very high sensitivity. Therefore, the amount of the photo acid generator (photosensitive agent) is required only to be sufficient for generating a catalytic amount of hydrogen ions. This makes it possible to enhance the transparency of the resist. As a result, the use of a chemically amplified resist makes it possible to form a resist pattern with a high aspect ratio. In the chemically amplified resist, the hydrolytic reaction by the acid catalyst is brought about while diffusing the hydrogen ions in the post exposure bake (PEB) step, and, therefore, temperature control and acid diffusion control in the PEB step is important.
In addition, recently, as a new lithography technology, there has been proposed a double patterning method in which formation and patterning of a photoresist layer are carried out two or more times.
FIGS. 15A to 15H are sectional views for illustrating an example of the double patterning method introduced in Japanese Patent Laid-open No. 2008-83537 (pp. 23, 24, 26 to 28, and 31 to 33; FIGS. 1 and 2) (hereinafter referred to as Patent Document 1). In this method, first, as shown in FIG. 15A, a functional material layer 102 to be patterned, a hard mask layer 103, and a resist layer 104 are formed over a substrate 101 in a laminated or stacked manner. Next, the resist layer 104 is selectively exposed to light through a mask 121, followed by development, whereby a resist pattern 106 having a plurality of trenches (width: d/4) 105 arranged at a pitch d is formed, as shown in FIG. 15B. Subsequently, the hard mask layer 103 is etched using the resist pattern 106 as a mask, followed by removing the remaining resist pattern 106. Consequently, a hard mask pattern 108a formed with a plurality of trenches (width: d/4) 107 is obtained, as shown in FIG. 15C.
Next, as shown in FIG. 15D, a resist layer 109 is formed on the hard mask pattern 108a in the manner of filling up the trenches 107. Subsequently, using a mask 122 positionally shifted by d/2 as compared with the mask 121, a second trench pattern formation is conducted in the same manner as above-mentioned. Specifically, the resist layer 109 is selectively exposed to light through the mask 122, followed by development, whereby a resist pattern 111 having a plurality of trenches (width: d/4) 110 arranged at a pitch d is formed, as shown in FIG. 15E. Next, the hard mask pattern 108a is etched using the resist pattern 111 as a mask, followed by removing the remaining resist pattern 111. As a result of the second trench pattern formation, there is obtained a hard mask pattern 108b in which a plurality of trenches (width: d/4) 107 and 112 are arranged at a pitch d/2 equal to one half of the pitch in the mask 121 used, as shown in FIG. 15F.
Subsequently, as shown in FIG. 15G, the functional material layer 102 is etched using the hard mask pattern 108b as a mask, to form a functional layer 113. Thereafter, the remaining hard mask pattern 108b is removed, as shown in FIG. 15H.
As above-mentioned, according to the double patterning method, a pattern with a pitch smaller than that obtainable by the single patterning method can be formed while using the same exposure apparatus and the same resist composition as used in the single patterning method. In the double patterning method according to the related art, however, it is normally necessary to provide the hard mask layer 103 and the like over the substrate. Besides, in order to pattern the functional material layer 102, the formation and patterning of a resist layer should be carried out at least twice and etching of the hard mask layer 103 should be carried out at least twice; thus, the number of steps to be conducted is large.
In order to easily carry out the double patterning, the pattern obtained upon the first pattern formation (in the above-mentioned example, the resist pattern 106) should have such a solvent resistance as not to be eluted or deformed by the solvent of the resist coating liquid used in the second pattern formation and should have such a resistance to exposure and development as not to be eluted or deformed by the second exposure and development. However, ordinary resist patterns cannot satisfy these conditions. Therefore, before proceeding to the second pattern formation, the pattern obtained by the first pattern formation should be transferred to a layer which is high in solvent resistance and in resistance to exposure and development (in the above-mentioned example, the hard mask layer 103). This is why the number of steps in the double patterning method according to the related art is large.
In view of this problem, Patent Document 1 proposes a novel pattern forming method in which a coating film is formed on a resist pattern obtained by pattern formation so as to protect the resist pattern, whereby the number of steps in the double patterning method can be reduced.
FIGS. 16A to 16F are sectional views showing the pattern forming method proposed in Patent Document 1. Patent Document 1 contains the following description.
In this method, first, as shown in FIG. 16A, a first resist layer 202 composed of a positive-type first chemically amplified resin composition is formed on a support 201. Next, the first resist layer 202 is selectively exposed to light through a mask 221, followed by development, to form a first resist pattern 204 having a plurality of line patterns (width: d/4) 203, as shown in FIG. 16B.
Subsequently, as shown in FIG. 16C, a coating film forming aqueous solution 205 containing a water-soluble resin and a water-soluble cross-linking agent is applied to the surface of the first resist pattern 204 by a dipping method or a coating method or the like. The water-soluble resin may be any resin that is soluble in water at room temperature. The water-soluble resin is preferably one selected from the group including acrylic resins, vinyl resins, cellulose resins, and amide resins. Among these resins, preferred are vinyl resins, and particularly preferred are polyvinyl pyrrolidone and polyvinyl alcohol. The water-soluble cross-linking agent is an organic compound having at least one nitrogen atom in its structure. The organic compound is preferably a nitrogen-containing compound having an amino group and/or an imino group in which at least two hydrogen atoms have been replaced by a hydroxyalkyl group and/or an alkoxyalkyl group. Among these nitrogen-containing compounds, preferred from the viewpoint of cross-linking reactivity is at least one selected from the group including triazine derivatives such as benzoguanamine derivatives, guanamine derivatives, melamine derivatives, etc., glycoluril derivatives and urea derivatives having an amino group or imino group in which at least two hydrogen atoms have been replaced by a methylol group or a lower alkoxymethyl group or both of them.
After the coating film forming aqueous solution 205 is applied, the coating film is subjected to a heating treatment. This accelerates the diffusion of the acid (hydrogen ions) from the first resist pattern 204, and a cross-linking reaction of the water-soluble resin and the water-soluble cross-linking agent accelerated catalytically by the hydrogen ion takes place at the interface between the resist pattern 204 and the coating film forming aqueous solution 205. By the cross-linking reaction, a coating film 206 is formed on the surface of the first resist pattern 204, as shown in FIG. 16C. The heating treatment temperature is preferably 70 to 180° C. With the heating treatment temperature set within this range, a rigid coating film 206 is formed. The heating time is not particularly limited. Taking the effect of the heating treatment and the stability of pattern shape and the like into consideration, however, the heating time is preferably in the range of 30 to 300 seconds, more preferably 60 to 180 seconds.
Next, the surface of the first resist pattern 207 provided thereon with the coating film is preferably washed with a cleaning liquid. This ensures that, even if the water-soluble resin is adhered to a region where the first resist pattern 204 is absent, the water-soluble resin is washed away or becomes very low in concentration. On the other hand, the water-soluble resin adhered to the surface of the first resist pattern remains intact there, since it has been cross-linked. Consequently, as shown in FIG. 16D, the coating film 206 is sufficiently formed on the surface of the first resist pattern 204, while the coating film 206 is not formed at all or is not substantially formed in the other regions. Thus, the coating film 206 can be formed on the surface of the first resist pattern 204 with high selectivity of coating. Further, the washing ensures that the coating film 206 has a thickness which is small and uniform. Specifically, when washing is conducted, a surplus of the water-soluble resin which is not cross-linked on the first resist pattern is removed, whereas the water-soluble resin boned firmly to the surface of the first resist pattern 204 by the cross-linking is left uniformly on the surface of the pattern. The thin film of the water-soluble resin on the nanometer level is formed in a uniform thickness, extremely accurately, and with high reproducibility. The thickness of the coating film 206 is preferably 1 to 30 nm.
Subsequently, as shown in FIG. 16E, a second resist layer 208 composed of a second chemically amplified resist composition is formed so as to fill up the cavities between portions of the first resist pattern 207 provided thereon with the coating film. Subsequently, as shown in FIGS. 16E and 16F, the second resist layer 208 is selectively exposed to light through a second mask 222, followed by development, to form a second resist pattern 209.
On the other hand, in recent years, researches have been vigorously made of integrated chemical systems for integrating operations necessary for chemical processes, by use of microchips in which fine liquid flow networks (microchannels) are formed on a glass substrate. A microchannel can be grasped as a fine chemical experiment space (unit operation space). When a substance is put into reaction or separated in the microchannel, a size effect becomes actual in the fine space, whereby drastic scale-down of not only the amount of substance to be treated but also the reaction time can be achieved. For instance, it has been reported that, in an example wherein a carcinoembryonic antigen (CEA) as a tumor marker used for diagnosis of large bowel cancer was determined by use of an immunodiagnostic chip utilizing an antigen-antibody reaction, the analysis time could be shortened to 30 minutes, as contrasted to 50 hours according to the related art (see Hideaki Hisamoto, Manabu Tokeiji, and Takehiko Kitamori, “Kagaku-to Kogyo” (Chemistry and Chemical Industry), 54, pp. 564 to 568 (2001), hereinafter referred to as Non-patent Document 1).
In these researches, at present, chips in which microchannels are formed in a glass substrate or silicon substrate by etching are used, taking chemical resistance and the like into consideration. However, glass substrates and silicon substrates have problems on a practical-use basis in that they are expensive, heavy, and unable to be disposed of by incineration. In view of this, Japanese Patent Laid-open No. 2005-265634 (claim 8; pp. 10 to 15; FIG. 1) (hereinafter referred to as Patent Document 2) proposes
a method of manufacturing a resin-made microchannel array, including the steps of:
forming a pattern of a resist on a substrate;
depositing a metal according to the resist pattern formed on the substrate, thereby forming a metallic structure; and
forming a resin-made microchannel substrate by use of the metallic structure.
In this method, the resist pattern is produced by photolithography, the metallic structure is produced by a vacuum evaporation method or a sputtering method and a plating method while using the resist pattern as a mold, and the resin-made microchannel substrate is produced by injection molding or the like using the metallic structure as a mold. Patent Document 2 describes that according to this method, ten thousands to fifty thousands of resin-made microchannel substrates, possibly no less than two hundreds of thousands of resin-made microchannel substrates can be produced by use of a single metallic structure, and, thus, resin-made microchannels can be obtained with good productivity, at low cost and with high accuracy.